Step 1
If you have any third party antivirus software and firewall disable them temporarily and make sure that the Windows Firewall is turned on. Then check if the issue reappears.Step 2
1. Open Run, and type in services.msc then press Enter.
2. In services window, locate Windows Defender service in the services list.
3. Verify that the Status is Started. If the Status column is blank,
right click on the service and select Start.
4 If you get error trying to force start the Windows Defender service, try to change the Startup Type to Automatic, and then restart the computer.

Glad I was able to answer your question. WD is an anti-malware component. When MS released MSE it includes AV and AM and automatically disables WD which should cause the actions you are seeing.

I believe in order to re-enable WD you would have to disable MSE, and MSE is considered the best app of the 2. The latest version of MSE for Vista and Win 7 is version 4. You might want to check this as well.

How can I find out what version of MSE I am running? I opened it and I don't find any indication there so I clicked on Help on that screen hoping to see the usual Help About but that wasn't anywhere to be seen on the web page that opened up.